Continental drift and plate tectonics

Alfred Wegener discovers continental drift

In the late 1500s Abraham Ortelius suggested that the Americas were “torn away from Europe and Africa … by earthquakes and floods…. The vestiges of the rupture reveal themselves, if someone brings forward a map of the world and considers carefully the coasts of the three [continents].” After him, a number of other geologists made similar observations, up until the 1850s.

Writing in 1889, Alfred Russel Wallace remarks “It was formerly a very general belief, even amongst geologists, that the great features of the earth’s surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had again and again changed places with each other.”

How could something as large as continents possibly move? At the time no one knew. There was yet no systematic search for evidence. The idea was mostly based on the shapes of the continents. So by the 1850s many geologists discarded the idea that continents could move. It wasn’t until Alfred Wegener (1880-1930) came along that research really began

Fossils exist in geographic patterns – this pattern implies that all of the continents must have once laid together.

Based on this evidence, Wegener proposed that over time, the continents slowly moved like this:

Initial rejection of Wegener’s hypothesis

Wegener’s theory of continental drift was not accepted for many years. Why?

* A plausible driving force was missing. (i.e. what could possibly push an entire continent through the Earth’s crust?)

* Wegener did propose a hypothesis about how continents could move, but he was incorrect about them. Although today we know that Wegener was right that the continents do move, he did not know how they did so.

* It is the nature of science to be skeptical of extraordinary claims. When one makes extraordinary claims, one must bring evidence to back them up. Wegener had begun the process of collecting evidence, but there was much more work to be done over the next 40 years.

Evidence eventually discovered

* Jigsaw Fit : The similarity in outline of the coastlines of eastern South America and West Africa had been noted for some time. The best fit is obtained if the coastlines are matched at a depth of 1,000 metres below current sea level.

* Geological Fit : When the geology of eastern South America and West Africa was mapped it revealed that ancient rock outcrops (cratons) over 2,000 million years old were continuous from one continent to the other.

* Tectonic Fit : Fragments of an old fold mountain belt between 450 and 400 million years ago are found on widely separated continents today. Pieces of the Caledonian fold mountain belt are found in Greenland, Canada, Ireland, England, Scotland and Scandinavia. When these land masses are re-assembled the mountain belt forms a continuous linear feature.

* Glacial Deposits : Today, glacial deposits formed 300 million years ago are found in Antarctica, Africa, South America, India and Australia. If the continents haven’t moved, then this would suggest an ice sheet extended from the south pole to the equator at this time – which is unlikely… [but] if the continents of the southern hemisphere are re-assembled near the south pole, then the Permo-Carboniferous ice sheet assumes a much more reasonable size.

* Fossil Evidence : There are many examples of fossils found on separate continents and nowhere else, suggesting the continents were once joined.

Scientists discovered mantle convection cells within the Earth: This is what makes the tectonic plates moves. Here are several animations and videos.

Continental rifts

The Great Rift Valley – a divergent plate boundary from the Afar Triple Junction, southward across eastern Africa. It is in the process of splitting the African Plate into two new separate plateshttp://en.wikipedia.org/wiki/Great_Rift_Valley

Modern theory of plate tectonics

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A history of supercontinents on planet Earth

From “A history of supercontinents on planet Earth”, Io9.com, Alasdair Wilkins
Continents are still on the move, and they’ll almost certainly continue to move until the Sun vaporizes our planet in five billion years’ time. In all likelihood, the continents will merge again to form a new supercontinent within in the next 250 million years, completing the latest turn of the supercontinent cycle.

The video below traces the movement of the continents through the end of Rodinia to the formation of Pangaea, and then on another 250 million years into our future:

As you can see, enjoy the Atlantic Ocean while you can, because it won’t be around forever.

Africa and North America will crash into each other, while South America is going to get cozy with Antarctica.

Australia will crash into China and southeast Asia, which really just sounds like the premise for a mildly offensive sit-com.

And Europe? Poor Europe looks like it’s headed for significantly colder climes, getting dangerously close to becoming the new North Pole.

This is one potential configuration, although there are at least three scenarios that geologists consider realistic. All of them have pretty awesome names:
Novopangaea, Amasia, and my personal favorite, Pangaea Ultima. …Here are some artist’s conceptions of all three:

Pangaea Ultima is probably the somewhat preferred theory of geologists, but there the Pacific plate does seem to be sliding underneath North America and Eurasia, which would mean the ocean itself with close if it continues on this present course. But that’s the problem – we’re trying to predict millions of years worth of of incremental movement based on a pitifully incomplete dataset. A best guess is about the most we can really expect.